linux-kernel - Re: [PATCH] dmatest: masking tests for channel capabilities

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Message-ID: <CAA9_cmcKehEhdeeRv7XrcNHBTxAcyf5cw6d=szMV8q0_BwHSFw@mail.gmail.com>
Date:	Tue, 18 Jun 2013 13:44:27 -0700
From:	Dan Williams <djbw@...com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Jubin Mehta <jubin.mehta@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Jon Mason <jon.mason@...el.com>
Subject: Re: [PATCH] dmatest: masking tests for channel capabilities

On Tue, Jun 18, 2013 at 1:01 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Tue, Jun 18, 2013 at 10:16 PM, Dan Williams <djbw@...com> wrote:
>> On Tue, Jun 18, 2013 at 10:34 AM, Jubin Mehta <jubin.mehta@...el.com> wrote:
>
>>> Would you like to have some changes regarding the configuration
>>> process for the module parameters of the dmatest?
>>
>> Yes, as a first step I would like to see a clean up of the the
>> configuration parameters to be available via
>> /sys/module/dmatest/parameters rather than /sys/kernel/debug/dmatest
>
> Do  you mean to enable write access to them?

Yes.

>
>> As for "run" and "results" I see Andy's point that those are a bit
>> awkward as parameters.  However, we do have trace points as a more
>> general mechanism for dumping events and data to userspace.  If we had
>> /sys/module/dmatest/parameters/run with a tracepoint for the result
>> line does that get us everything we need for automation?  I can see
>> more tracepoints beng added to get some perf metrics out of the tests.
>
> I'm not familiar neither with perf, nor with tracepoints. Could you
> elaborate and show here the scheme how it should work? How we will get
> results? In what form?
>

It would be very similar to what it does now except using generic
functionality.  At a high level you would have a tracepoint that emits
something like:

dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)

...and that message shows up in the ftrace buffer when it fires.

These articles are a good starting point.
https://lwn.net/Articles/379903/
https://lwn.net/Articles/383362/
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